Wireless communication protocols and devices, such as Long Term Evolution devices, have been introduced that allow the wireless communication of concurrent voice and data services. Typically, this involves a device with two transceivers and two respective antennas, one for each service. However such concurrent communication can cause cross coupling of signals, which can result in intermodulation distortion (IMD) related issues. As a result, vendors of such devices desire to provide a minimum amount of isolation between antennas to reduce cross coupling. However, this can be problematic in a small communication device, such as a mobile handheld device, where the package size and antenna orientation parameters are set to optimize ergonomic considerations. Simulations have been performed, using standard packaging of handheld mobile communication devices, where the isolation between different antenna structures upon the same device can drop to less then 3 dB in many cases, which is unacceptable for IMD performance.
One technique for increasing isolation between antennas is to use a circulator canceller in order to increase channel isolation. Although this technique works, it has only been implemented in large communication devices using a large, tuned and shielded circulator, which is expensive, and has only been operable for very high power levels. None of these operational parameters can be carried over to a small handheld wireless device using a small, low-cost circulator. In particular, miniature circulators and isolators are inherently low performance, narrow band devices due to limits on size and magnet configuration, and these miniature circulators have minimal shielding, allowing their performance to be influenced by nearby fields.
Accordingly, there is a need for to provide antenna isolation in a small wireless communication device that uses commercially available low-cost circulators.
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